Hello, I want to install new circuits in my basement and I want to do
it off of an electrical sub panel. The subs i see are only 1 phase.
How to I tap into the main box? Do i still use a double pole
breaker? Single pole breakers only go upto 30 amps. I want to run 4
separate circuits off the new box. Thanks.
On Jan 30, 3:52 am, email@example.com wrote:
I had the same idea to power a tankless water heater but found it
better for My place to upgrade to a larger,higher amp panel..
Members here might need more info as to what Your existing set-up
is to give You the best help;;What amp is the main in Your box? Is the
existing panel full or are there unused circuits? Are You adding 15
amp circuits? 20 amp? larger? What amp is the service from the meter
outdoors? Do You have specific uses in mind for the new circuits so
the amp draw can be estimated or just general use?
I'm not a Sparkie but am interested after My recent upgrades..
As Dean said, you need to furnish a lot more info. When you say that subs
you see are only 1 phase, you're correct, it's rare for a residential
service to have 3 phase. Are you looking to connect a machine that requires
3 phase or just not familiar with the terminology? You will need to know the
size of the existing service and some idea of what's attached to it
currently. You'll also need to provide details of what you're looking to
connect in the basement, to determine the feeder and panel size. BTW single
pole breakers do come in larger than 30 amp, however its usually more
practical to build the device to operate at 240 volt and keep the amperage
On Jan 30, 1:52 am, firstname.lastname@example.org wrote:
I believe you mean "legs" ..........or do you really mean
I suggest using a Square D QO Load Center..the one I'm thinking of has
8 breaker slots (100 or 125 amp rating; I think) & is feed 220V ( 2
legs) via a double pole breaker from the main.
Now you have sub panel that is mini version of your main...two legs,
across which you have 220V when you use a double pole breaker.
If you really mean phases & you're trying to get 3 phase power out of
a residential service you're sol unless you buy a phase converter.
but I'm pretty sure the first part of my answer will get the job done
for you, since it seems like you're just looking for more amps for a
heavier drawing load....and the way to get that is on a 220v circuit.
On 30 Jan 2007 01:52:21 -0800, email@example.com wrote:
Actually most sub panels do use 2 hot legs (240v and 120v),
don't confuse that with the term, "single phase". That is really one
"phase", center tapped to give you two 120v circuits.
You use a 2 pole breaker in the main panel and be sure to run a 4 wire
feeder to the sub. Buy the extra ground bus kit. Leave the bonding
screw off the neutral bar, connected to the white wire in the fereder
and it stays insulated. The bare/green wire in the feeder goes to the
supplimental bar and that is where your ground wires go.
This is still singe phase. The fact that it is center tapped does not
add a phase. "Two phase" does exist but most people will never see it.
That has the phases shifted by 90 degrees and uses 4 circuit
On Tue, 30 Jan 2007 21:01:59 -0500, firstname.lastname@example.org wrote:
Making that center tap the reference point (which seems logical since
it's grounded) and examining the voltages on the other 2 conductors,
you now have 2 points out of phase with other. 2 phases.
I even looked up the definition of "phase" again. Nothing about it
excludes 180-degree separation.
I haven't really seen it, but have read about it.
That's definitely 2 phase. That does not limit "2 phase" to that. That
would be like saying that the definition of "money" is "$15" (allowing
no other amounts to qualify).
There's also 4-phase, and I have seen that but only for driving
As previously posted 2 phase power is very rare now days. Typical
service panels are a 3 wire single phase system. It is very common to
incorrectly refer to this as "two phase". Follow the link for an
On Wed, 31 Jan 2007 23:11:50 -0500, email@example.com wrote:
Of course it has NOTHING to do with what I want. It has to do with
what the WORD "phase" actually means.
BTW, I never said I don't call it "split phase". I just said it was 2
Just to be sure we're still talking about the same thing, it's AC from
a center-tapped transformer secondary with the center tap grounded?
Are you using a definition of "phase" that DOESN'T apply to the
120/240VAC electrical system? What it that definition?
BTW, here is one definition:
3. A measure of how far some cyclic behavior, such as wave motion,
has proceeded through its cycle, measured in degrees or radians. At
the beginning of the phase, its value is zero; at one quarter of its
cycle, its phase is 90 degrees (?/2 radians); halfway through the
cycle its value is 180 degrees (? radians), and so on. ? The phase
angle between two waves is a measure of their difference in phase. Two
waves of the same frequency that are perfectly in phase have phase
angle zero; if one wave is ahead of the other by a quarter cycle, its
phase angle 90 degrees (?/2 radians); waves that are perfectly out of
phase have phase angle 180 degrees (? radians), and so on. See more at
Source: American Heritage Science Dictionary (c) 2002
Of course it's a lot easier to understand than to explain.
AC is definitely "cyclic behavior", and when you examine the 2
nongrounded conductors at he same time you see the cycle at 2
different points. You can measure the voltage between the HOT wires of
2 different 120V outlets (120V hot to neutral). You get either 0V or
240V. That's enough to tell you something's going on.
120V is not the same as 120V (measured at different outlets). What's
different about it?
It is just a garden variety single phase 120/240 transformer that they
add a second one to and trick motors into thinking it is 3 phase.
Generally they don't use the 3d transformer to make a true delta.
If they wanted to spend that much money you would get 3p wye.
You see it in light industrial areas where most of the load is single
phase on a big 1p transformer and a second only supplies the "red" leg
for the 3p load. (actually identified orange) As long as you never put
L/N loads on the 208v red leg it works fine.
I have seen a lot of the two transformer open delta and three transformer
wye services, but I have also seen quite a few three transformer closed
delta systems. It seems to depend on the relative loads. The open delta
seems to be used where the three phase load is fairly light and the closed
delta where there is a heavy three phase load but 120/240 single phase
service is also required. It may be a regional thing and I think the delta
connection is becoming rarer and is being replaced with a separate single
phase transformer where 120/240 is required.
Open delta lowers the transformer power factor so the the transformers
have to be derated - probably why open delta is generally light loads.
Wye is easier to balance which is a good reason to use it instead of
delta. (You can also get wye with 2 transformers in a Scott or T
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